1. Technical Field
The present invention relates generally to ATM (Asynchronous Transfer Mode) multi-node networks and more specifically to a system and method for enabling the surveillance, through the nodes and switching pieces of equipment forming the network, of any switching node port from any convenient remote access point.
2. Description of the Related Art
Broadband ISDN (Integrated Services Digital Network) was an attempt to set up a single unified, worldwide high-speed network in place of the multiplicity of existing networks for different applications. On one hand, the new, universal network was intended to replace the functions of current speech, data and television networks and, on the other hand, to provide enough scope for the implementation of future communications technologies.
The first work on standards for the universal network of the future was begun by CCITT (International Telegraph and Telephone Consultative Committee) in the late 1980s, under the title “B-ISDN”. B-ISDN is based on ATM which is a data transmission technique belonging to the family of cell switched systems (cell relay). Unlike packet-switched systems, in which data packets of variable length can be multiplexed over a line interface, the length of a cell relay data packet is fixed and simply referred to as a cell. ATM is a specific implementation of cell relay and an integral element of the CCITT specification for B-ISDN.
ATM, as the name suggests, utilizes an asynchronous time division multiplexing scheme so that the data streams to be transmitted are converted into fixed-size cells and transferred asynchronously over a same physical medium between network nodes. The allocation of the units of information to the different transmission channels is carried out using numerical channel identifiers attached to each cell under the form of a VPi (Virtual Path identifier) and a VCi (Virtual Channel identifier).
ATM is a cell switching technology in which cell-switch units within network nodes route cells towards their final destination and which may also buffer the cells before transmission to a next node. Cell switching implies that a temporary end-to-end transmission path must be provided before any data can be transferred between sender and receiver. Thus, cell-switched networks can take advantage of the greatly varying bandwidth requirements in data communications by allocating unused transmission capacity to other virtual connections on an as needed basis.
Since cell-switched networks create only virtual transmission links (over a common physical transmission line), it is possible for cells to be lost if the memory capacity of the switching nodes is exceeded. This transfer procedure, which first requires a (virtual) link to be set up between the users, is said to be connection-oriented (as opposed to connectionless like e.g., IP the Internet Protocol). Links are categorized as either PVC (Permanent Virtual Connection), in which the link is set up once for all, as SVC (Switched Virtual Connection) in which the link is set up dynamically, on demand.
It is only after such a connection has been established, be it permanent or dynamic, that sending station can forward its data, under the form of cells, to the receiving station which receives them in the same order. However, if problems occur during the transfer of the data such as a buffer overload, resulting in discarded cells or the receipt of faulty or misdirected cells, the problem is immediately reported to the other end, which can react appropriately (generally by repeating the transmission of the cells forming a message so that the problem can be handled by the error recovery routines of the higher level protocols).
Thus, ATM switching units are key elements in any B-ISDN network. The fact that all ATM cells are the same size is exploited to implement multiport switching fabrics (typically 16×16 or 32×32) based on various efficient architectures which, when combined with the latest sub-micron fabrication processes, permit very high performances and aggregate throughputs which must be expressed in terabits per sec (1012/sec). The remaining task of the switching fabric and switches at each node of a network then becomes to provide transmission paths between the input ports and output ports requested at any given time in such a way that the fewest possible conflicts occur.
For example, an internal conflict to a switch fabric may occur if two or more cells are competing for the same output port at the same time. Despite every effort being made during the architecture and design phases of switches and cell-networks in general to provide the necessary mechanisms to handle the data flows without conflicts, traffic congestion is inevitable in a node when either overall traffic is increasing or when a traffic spike occurs at the node at a given instant. Also, flaws and shortcomings that may be present in some of the numerous hardware and software pieces that together implement a network, although not serious enough to prevent the network from operating reasonably well and, in any case, at the satisfaction of the end users, may also trigger occasionally some of the previously mentioned problems such as cell discarding.
Therefore, it is of utmost importance for those in charge of running and maintaining such an ATM network to be able to watch it and analyze it, if not constantly, at least any time it is necessary, from any convenient access point, without having to disturb user traffic whatsoever. Moreover, because ATM networks are typically used nowadays to implement high performance backbones of many medium or large networks (contradicting the initial expectation that ATM would become the universal means to transport data, voice and all multimedia information, up to desktop) quality performance must be ensured with the proper tools, such that the high level of quality assurance expected of an ATM network is indeed delivered.